Field of the Invention
The present invention relates to a wood-based material board, especially in the form of a wood/plastic composite material, and to a process for producing such a wood-based material board.
Description of Related Art
In a multitude of floor coverings, a fundamental problem in use is the material damage caused by moisture and/or water, said material damage including not just material destruction but also deterioration in the product properties or the occurrence of odors. Whereas the occurrence of watermarks, odors or, in the worst case, mold is observable in the case of textile floor coverings as a result of these specific conditions, it is usually surface impairments such as mattness that are observable in the case of varnished products.
As well as textile floor coverings, the use of wood-based material boards, for example in the form of wood fiberboards in different configurations, for use as a floor laminate or for cladding of walls or else in the production of furniture has long been known. For example, wood fiberboards are used in the form of medium-density wood fiberboards (MDF boards), high-density wood fiberboards (HDF boards), particleboards or OSBs (oriented strand boards), which are obtained by compression of appropriate wood fibers or shavings with a thermoset polymer resin as binder.
A particular problem in the use of the wood fiberboards mentioned lies in the sensitivity of the wood fibers or wood shavings used to high air moisture contents and direct contact with water. Whereas this problem can be controlled relatively easily by means of construction or technological measures in the case of furniture or products for interior fitting, this is frequently much more problematic in the case of floor coverings, for example laminate floors based on wood or wood-based materials.
Floor coverings based on wood or wood-based material boards, such as laminate floors or ready-made parquet, react quickly to contact with water by swelling and/or changes in dimensions which can evolve from slight edge swelling as far as destruction of the fitting structure. One cause of this is exposure to water-based care products, which are in some cases used very frequently and very intensively. High air humidities can also trigger comparable processes. Furthermore, the floor covering is typically also in direct contact with the components of the building, for example concrete floors/screed or walls, which can likewise transport moisture into the floor covering. For this reason, in the production of the abovementioned wood-based material products, low-swelling woods or wood-based materials are employed, which can alleviate the problems described, but not entirely remedy them. In some cases, inorganic base boards are also used for production of products having wood surfaces, but there can be problems here with bonding, processing or laying.
The more densely the wood or wood-based material has been consolidated in the production of the product, the more serious the moisture damage. As a result, the swelling pressure on contact with water is greatly increased. This explains, for example, the distinct reaction of laminate floors or varnished wood-based materials to direct contact with water. A multitude of measures (swell-tempered boards, edge sealing, etc.) has led to improvements with regard to sensitivity to water/moisture, but has not been able to completely solve the problems.
As an alternative to the use of laminate floors with the swelling problem mentioned, there was increasing use in the past of floor coverings based on polyvinyl chloride (PVC), which have very low to zero swelling. However, disadvantages of the use of PVC floors are their high sensitivity to scratching and their tendency to creep, which leads to rapid wear and an unsightly appearance of the floor covering especially in areas with high traffic (for example sales areas).
For these reasons, wood/plastic composites (WPCs) have frequently been used in the past as backing materials for wood products. These backing materials have very low swelling of less than 3% and high dimensional stability.
WPCs are thermoplastically processible composite materials based on wood flour or wood shavings and thermoplastic polymers, to which further additives may be added if appropriate. The mixtures of wood fibers and thermoplastics are melted and processed to agglomerates. Later in the production process, the agglomerates are melted in extruders and processed to give boards of relatively small size format. The width of the boards here is usually within a range of less than 1 meter, caused by the production process in an extruder. The productivity per hour is also in a low single-digit square meter range, and so the combination of low productivity and limited board size causes relatively high costs of the WPC boards thus produced.
The fact that the wood component has to be dried to a moisture content of less than 5 wt %, better even to less than 1 wt %, likewise does not contribute to low costs. Higher moisture contents lead to formation of water vapor in the process and hence to blister formation in the product. A further serious disadvantage is that the wood used has to be free of sand and minerals. Such disruptive materials would otherwise destroy the extrusion tool.
This correspondingly gives rise to the disadvantages of low productivity, limited board size and hence a costly process.
It is therefore a technical object of the present invention to remedy the disadvantages described and to provide wood-based material boards having a low swelling of, for example, less than 3% in more variable and larger size formats and with higher productivity. These wood-based material boards are subsequently to be usable as base boards, including for production of products for applications with elevated occurrence of moisture.